Many SMPS applications require the output current to be either limited to or maintained at a particular value. It is desirable to employ primary-side sensing for a number of reasons, for example isolation. Many techniques have been described for primary-side voltage sensing—see, for example, our earlier published applications GB 2,438,464 and GB 2,438,465 (incorporated by reference) as well as, for example, U.S. Pat. No. 6,900,995 (iWatt) but it is less common to employ primary-side sensing for output current regulation.
We have previously described primary-side output current sensing/regulation techniques in GB 2,439,997 (U.S. Pat. No. 7,342,812), GB 2,439,998 (U.S. Pat. No. 7,525,823) and EP 1835605—hereby incorporated by reference—and we now describe techniques for improving the accuracy of such output current sensing/regulation, broadly speaking by improving the accuracy/reliability of the timing signals involved.
Other background prior art can be found in US2006/0285365, WO2007/041897, U.S. Pat. Nos. 6,977,824, 6,842,350, US 2006/034102, US 2005/285587, US 2006/077697, US 2004/196936, U.S. Pat. Nos. 5,218,521, 7,288,924, 5,463,662 and 7,016,204.